Apparatus for seeking a track of an optical disk in which information is recorded

Abstract

A track-seeking apparatus for an optical disk drive seeks a target track by counting track crossings according to a track-crossing signal. The track-seeking apparatus also has means for detecting the ID fields on the disk and substituting a simulated track-crossing signal for the track-crossing signal in these fields, thus enabling high-speed seeking without track-count errors.

What is claimed is: 
     
       1. A track-seeking apparatus for use with an optical disk in which information is recorded in spiral or concentric circular tracks having data fields with pregrooves and identifier fields with pits, comprising: means for rotating said optical disk;   a pick-up unit for focusing a light beam onto said optical disk, detecting the light reflected from said optical disk, and converting it to at least one pick-up signal;   driver means for moving said pick-up unit parallel to said optical disk and across said tracks; and   a control circuit for receiving at least one pick-up signal and at least one of control signals, one of said control signals being a seek count signal indicating the number of tracks the light beam must cross to reach a target track, and controlling said driver means according to said at least one pick-up signal and said at least one of control signals so that said driver means causes said pick-up unit to move from a current track to the target track, wherein said control circuit comprises: track-crossing detection means for detecting track crossings by said light beam and generating a track-crossing signal;   velocity detection means for detecting the pick-up velocity at which said pick-up unit is moving and generating a pick-up velocity signal;   simulation means for generating a simulated track-crossing signal according to said pick-up velocity;   identifier gating means for detecting when said light beam is focused on one of said identifier fields;   a switch controlled by said identifier gating means, for producing a track detect signal that consists of said track crossing signal when said light beam is not focused on one of said identifier fields, and said simulated track-crossing signal when said light beam is focused on one of said identifier fields; and   means for terminating the seek operation when, as a result of counting the track detect signal, said terminating means determines that said number of tracks indicated by said seek count signal has been crossed.     
     
     
       2. A track-seeking apparatus according to claim 1, wherein said identifier fields contain track address information and said apparatus further comprises an address reader for receiving said at least one pick-up signal and extracting the track address information, and means for examining, upon termination of the seek operation, whether the track the light beam is focused on is the target track. 
     
     
       3. A track-seeking apparatus according to claim 2; further comprising an input unit for receiving said track address information and external commands and generating the control signals. 
     
     
       4. A track-seeking apparatus according to claim 3, wherein said input unit is a microcomputer. 
     
     
       5. A track-seeking apparatus according to claim 1, further comprising a track counter for receiving said seek count signal and said track detect signal and generating a remaining track count. 
     
     
       6. A track-seeking apparatus according to claim 5, further comprising velocity control means for controlling said driver means according to said pick-up velocity and said remaining track count. 
     
     
       7. A track-seeking apparatus according to claim 1, wherein said pick-up unit has a dual photodetector for detecting the intensities of two separate parts of said reflected light and generating as pick-up signals a sum signal corresponding to the sum of said intensities and a difference signal corresponding to the difference of said intensities. 
     
     
       8. A track-seeking apparatus according to claim 7, wherein said track-crossing detection means comprises: a first comparator for receiving said difference signal and generating a binarized difference signal that assumes one of two values depending on whether or not said difference signal exceeds a certain threshold; and   a pulse generating circuit for receiving said binarized difference signal and generating a track-crossing pulse on the rising edge of said binarized difference signal.   
     
     
       9. A track-seeking apparatus according to claim 7, wherein said identifier gating means comprises; a second comparator for receiving said sum signal and generating a binarized sum signal that assumes one of two values depending on whether or not said sum signal exceeds a certain threshold, said threshold being high enough that it is exceeded only when said light beam is focused on one of said identifier fields; and   a monostable multivibrator for receiving said binarized sum signal, generating a pulse signal with a duration equal to or greater than the length of time said light beam remains in said identifier field, and sending said pulse signal to said switch.   
     
     
       10. A track-seeking apparatus according to claim 7, further comprising: a low-pass filter for receiving said difference signal and generating a filtered difference signal from which high-frequency components produced by said identifier field are removed; and   mode control means responsive to a mode control signal for selecting a first mode in which said track detect signal consists of said simulated track-cossing signal, or a second mode in which said track detect signal consists of said track-crossing signal and said filtered difference signal is substituted for said difference signal in said control circuit.   
     
     
       11. A track-seeking apparatus according to claim 10, wherein said second mode is selected only when said pick-up velocity is less than a certain velocity threshold. 
     
     
       12. A track-seeking apparatus according to claim 10, wherein said second mode is selected only when said remaining track count is less than a certain count value. 
     
     
       13. A track-seeking apparatus according to claim 10, wherein one of the control signals is the mode control signal, said low-pass filter comprises a resistor and a capacitor, and   said mode control means comprises:   a switch inserted between said resistor and said capacitor, and controlled by said mode control signal;   an inverter for inverting said mode control signal;   an AND gate for ANDing the output of said inverter with the output of said identifier gating means.   
     
     
       14. A track-seeking apparatus according to claim 10, wherein said track-detecting means comprises: a hysteresis comparator for receiving said difference signal or said filtered difference signal and generating a binarized difference signal that assumes one of two values according to a pair of input thresholds: an upper threshold at which said binarized difference signal changes from its lower to its higher value; and a lower threshold at which said binarized difference signal changes from its higher to its lower value; and   a pulse generating circuit for receiving said binarized difference signal and generating a track-crossing pulse on the rising edge of said binarized difference signal.   
     
     
       15. A track-seeking apparatus according to claim 1, wherein said velocity detecting means comprises; an up-counter for measuring the interval between successive pulses in said track detect signal;   a register for receiving and storing the count value in said up-counter at each pulse in said track detect signal; and   a read only memory for receiving said count value from said register and converting it to a velocity value.   
     
     
       16. A track-seeking apparatus according to claim 15, wherein said simulation means comprises a down-counter for receiving said count value from said up-counter and said track detect signal from said switch, counting down from said count value starting when said track detect signal is received, and generating a simulated track-crossing pulse upon reaching zero. 
     
     
       17. A track-seeking apparatus according to claim 1, further comprising an input unit for receiving track address information contained in said identifier fields and generating the control signals, a track counter for receiving said seek count signal and said track detect signal and generating a remaining track count, and velocity control means for controlling said driver means according to said pick-up velocity and said remaining track count, wherein one of the control signals generated by said input unit is a direction signal, and said velocity control means comprises: reference velocity generating means for receiving said remaining track count and generating a reference velocity signal;   subtractor means for receiving said pick-up velocity signal and said reference velocity signal and generating a velocity difference;   an exclusive OR gate, the inputs of which are said direction signal and the most significant bit of said velocity difference; and   digital-to-analog converting means for receiving said velocity difference signal with the output of said exclusive OR gate substituted for the most significant bit and generating an analog velocity error signal.